allele: One of several possible values that may exist for a genetic marker. Here it means the specific number of repeats at a given STR location on the Y-chromosome.
base: One of four molecules that, in combination with a phosphate, are the building blocks of DNA. They are adenine (A), cytosine (C), guanine (G), and thymine (T) and, when paired with their complements (A with T and C with G), form the ladder rungs of the DNA molecule. Each segment of genetic code is represented by a specific arrangement of a group of these molecules.
chromosome: An arrangement of DNA that contains the coded information cells need to function. The human cell contains 46 chromosomes, 22 pairs of which half of each pair is received from each parent, plus two sex chromosomes which are either two X-chromosomes in females, or an X- and a Y-chromosome in males.
DNA: DeoxyriboNucleic Acid - The double stranded molecule that encodes genetic information. It is made-up of phosphate, deoxyribose and four bases; adenine(A), cytosine (C), guanine (G), and thymine (T).
haplogroup: A cluster of people who share the same mutation and whose ancestry will converge to a single individual known as the founder. In the analysis of Y-chromosomes, haplogroups are generally defined by SNPs. Haplogroups are also know as clades.
haplotype: An individual's complete set of analysis results for those markers which were tested. In Y-chromosome analysis, a haplotype is expressed as a series of numbers, where each number represents the allele value for a specific STR, which may then be compared to other haplotypes to determine relatedness. In cases where individuals are shown to be related, it can be used to statistically estimate the number of generations between them and their Most Recent Common Ancestor (MRCA).
marker: A specific location on the Y-chromosome with known characteristics, and where genetic variation is present (e.g., the location of a SNP or STR). These markers can then be used for comparison purposes.
mitochondria: An ancient parasitic bacteria, present in all human cells, that produces energy for the cell. It has its own DNA which is passed, via the human egg, from mother to child without recombining. Because recombination does not take place, mitochondria DNA is very stable, a characteristic which makes it ideal for tracing genetic histories.
modal: The most common, and therefore usually the oldest, haplotype, which represents the set of marker values that defines a specific genetic line, along with its later descendant variations. Because of our limited number of samples, we are using the term to represent the probable haplotype of the Most Recent Common Ancestor (MRCA). Consequently, none of our test results may actually match the indicated modal.
MRCA: Most Recent Common Ancestor - The most recent ancestor common to two individuals, such as a shared grandparent or great-grandparent, from whom the two individual's separate lines diverged.
nucleotide: A combination of one of the four DNA bases (i.e., adenine, cytosine, guanine, and thymine) plus a phosphate. Nucleotides are the building blocks of the DNA molecule.
SNP: Single Nucleotide Polymorphism: A type of polymorphism that takes place at a single nucleotide at a specific location on the Y-chromosome. This mutation is the result of a replacement, deletion, or insertion of a single nucleotide. It occurs so infrequently that it is used to define haplogroups.
STR: Short Tandem Repeats: A type of polymorphism where a short pattern of nucleotides, usually 1 to 6 in length, in the non-coding region of the Y-chromosome, is repeated a number of times in tandem. The number of repeats is the allele value for that STR.
Y-chromosome: One of the two so-called sex chromosomes, which determines the gender of a human fetus. Females have two X-chromosomes, while males have an X and a Y. Only males have a Y-chromosome and if an egg is fertilized which a sperm containing a Y-chromosome, it too will be male. If not, it will be female. Since the Y-chromosome is thus passed from father to son, it is ideal for tracing male genetic histories.
Version: 103; Created on Saturday, September 26, 2009 at 4:00 pm